Spin-exchange NMR spectroscopy in studies of the kinetics of enzymes and membrane transport

Spin-exchange NMR techniques enable the measurement of the rates of exchange of solutes between chemically or physically distinct sites in reactions taking place at chemical equilibrium. The time scale of the events that are able to be investigated lies in the neighbourhood of 1 s. The earliest studies in this area of NMR spectroscopy involved chemical reactions in vitro but the procedures have been adapted to the study of enzyme-catalysed reactions both in vitro and in vivo, and more recently to transmembrane exchange processes. The emphasis in this review is on the various types of spin-exchange experiments, the analysis of data derived from them, estimates of uncertainty in measured rate constants, and their shortcomings. Those methods given special attention are saturation transfer, two-dimensional exchange spectroscopy (2D EXSY), the 'accordion' experiment and 'overdetermined' one-dimensional exchange spectroscopy.